1. Field of the Invention
Embodiments of the present invention generally relate to an apparatus and a method for processing semiconductor substrates. Particularly, embodiments of the present invention relates to methods and apparatus for trench and via profile modification prior to filling the trench and via.
2. Description of the Related Art
With continues decreasing of semiconductor device dimensions, trench or via structures formed on a semiconductor substrate during fabrication become increasingly narrow and high in aspect ratio. Narrow opening and high aspect ratio usually present difficulties and challenges for subsequent material filling process. As a result, voids are more likely to form in the filling material because the narrow openings would be pinched off during filling process.
The problem becomes more pronounced when a liner, barrier, or seed layer is requested for the filling process. The liner, barrier or seed layer is usually deposited on the trench or via structure using a physical vapor deposition (PVD) process. To achieve a complete coverage over the trench or via surfaces, overhangs usually form near an entrance of the trench or via. The overhangs worsen the pinch off in the subsequent material filling causing more voids formed in the filling.
FIGS. 1A-1B schematically illustrate problems in trench and via filling. FIG. 1A schematically illustrates a partial sectional side view of a substrate 10. A trench structure 2 is formed in a first material 1. A barrier layer 3 is then deposited over the trench structure 2. The barrier layer 3 is thicker near an entrance 8 of the trench structure 2 and forms overhangs 4 near the entrance 8. The overhangs 4 further narrow the entrance 8.
FIG. 1B schematically illustrates a material filling result of the substrate 10 of FIG. 1A. The entrance 8 is closed up by a filling material 5 prior to filling in the rest of the trench structure 2 forming a void 6 in the trench structure 2. The void 6 is usually undesirable especially when the filling material 5 is a conductive material (copper or aluminum) for interconnect, Germanium-Selenium-Tellurium (GST) fill for phase change memory cell, gate metal filling for metal gates.
Conventional fabrication process generally uses a sputtering process to modify the entrance 8 prior to depositing the filling material 5. As shown in FIG. 1C, positive ions 6, such as positive argon ions, generated in a plasma chamber are accelerated towards the substrate 10. The positive ions 6 gain momentum during acceleration and strike top surfaces of the substrate 10. The ions 6 physically dislodged the overhangs 4 to open up the entrance 8, as show in modified profile 7. However, the ions 6 also strike other areas outside the overhangs 4 damaging the substrate 10. Additionally, the dislodged particles generated during sputtering require additional cleaning process and may still become potential source of contamination for subsequent processing.
Therefore, there is a need for methods and apparatus to modify trench and via profile before material filling with increased efficiency and reduced damage.